The choice of baseline affects how we see warming | Data Bytes

One of the best measures to understand warming is through temperature anomalies. A temperature anomaly is the departure of the temperature for a particular year from a baseline. Positive anomalies indicate warmer than average conditions, while negative anomalies indicate cooler conditions when compared to the baseline.

This baseline or reference period is also referred to as the Long Period Average (LPA), and represents the average climatic conditions over a multi-decadal period of typically 30 years when measuring changes in temperature.

Temperatures today are typically measured against a reference period of 1991-2020, which is the baseline now in use by the India Meteorological Department, the official source of climatological data in India. However, looking at a range of baselines can provide important insights.

Using older baselines, such as 1951-1980, produces larger positive anomalies for present day temperatures with the anomaly estimated to be 0.98°C in 2024. More recent baselines, such as 1991-2020 produce smaller anomaly values for the same year with anomalies reducing to around 0.65°C. An intermediate baseline of 1981-2010 shows warming of a magnitude in between the two at approximately 0.78°C for 2024.

Updating baselines is important for climate monitoring because newer reference periods represent the current climatic conditions experienced by populations better. At the same time, older baselines highlight the cumulative scale of long-term warming. All baselines, however, show a warming trend.

Read more about what is driving rising temperatures in India.